I am trying to diagnose the suspension problem on the (new to us) 61k-miles 2004 SL500 (US).

We bought it from a couple who rarely drove it and it was sitting unused at least for a year before we bought it.

Symptoms:
1. previous owners say the front would sag completely but sometimes would lift back up after the car is on
2. the front (both sides) was completely down when we bought it and never went up since (drove it ~40miles on super-slow roads and left idling for 10-15 minutes couple times)
3. the rear appears to be at normal height and doesn't sag at all (rear valve-block shut-off valves must be in excellent condition)
4. front struts are visually in perfect condition
5. height-control doesn't do anything (when stopped in P, N, D, R or after driving slowly a few feet back and forward)
6. visually, the ABC liquid is not circulating (pulled the filter out while car is on and shifting through gears - and NOT seeing the liquid pouring out of it)
7. when we bought it, the liquid was slightly low. By mistake we put too much liquid in. After driving ~40 miles on slow-roads and AFTER we left it parked overnight at home all excess liquid did overflow from the tank (but didn't overflow while driving)
8. power-steering works perfectly
9. dashboard is red with "ABC" and "Car too low"
10. Red "Brake" is also illuminated but break-fluid is at level. Red "Break" does not disappear even after shorting the break-fluid-level sensor.
11. Front accumulator and front valve-block visually look fine and have no leaks.
12. We lifted driver-front corner and tried to change height (with gear in P, N, D, R but not moving, of course) - nothing happened either.

I am puzzled at how to troubleshoot it from here and will appreciate any advice.

The system appears to be completely off, because (5) height-control does nothing and (6) liquid is not circulating.

One guess is that it self-shut-down after detecting low-pressure, which explains height-control doing nothing and rear not moving up/down and not sagging.

Both front-sides being completely and equally down is puzzling. Are both front-valve-block's shut-off-valves equally worn? Strange coincidence.

If system is completely off, why would excess liquid overflow while the car was sitting overnight given that rear didn't sag and car is on even surface?

I am willing to give ABC-repair a try before doing a conversion. I will be grateful for any insight or ideas.

 

The first thing I would do is either get a Star Diagnostic system of your own or take it to a shop with one and read out the pump pressure.

As someone who is also new to the R230 and ABC, here’s my opinion, for whatever it’s worth.

I suspect Star Diagnostics will show very low output pressure from the pump, meaning it is dead. The ABC computer is keeping the lock valves in the valve blocks closed due to lack of system pressure and this is keeping the rear end raised. Since the dead pump cannot build pressure it cannot raise the car or circulate fluid through the system.

 

It is essential to have Mercedes' proprietary Star Diagnosis System (SDS) to troubleshoot many ABC problems. That is the case here. EDIT: I see the reply above posted two minutes before mine seems to echo my sentiment regarding SDS. Also, I personally would not trust any tech to solve an ABC issue which may be as complex as this one.

Clones of the system are sold on aliexpress.com, and a basic system that will meet the needs of maintaining an R230 can be had for as little as $250.

That is abnormal and indicative of an issue which may be the source of your ABC trouble.

It is my guess that if the pump can not meet the system's operating pressure of c. 190 bar, then no oil will circulate. If that is the case, then I believe the pump is worn or defective, but in theory it may be possible for it to be caused by something else.

In order to control the system hydraulic pressure there exists a throttle valve before the ABC pump which regulates the quantity of oil delivered to the pump. It seems highly unlikely to me, but I suppose it is plausible for the throttle to not function and be clogged with debris even though the oil returning to the pump reservoir is filtered. This would starve the pump of oil.

To diagnose the cause SDS can show you the hydraulic pressure being developed by the pump. It also has a diagnostic routine to test the throttle operation.

If this is a false indication, then one of the four level sensors located at each strut is defective, and SDS can identify which one. Otherwise, it is a consequence of the car being low and its inability to rise.

There is a fault in the SBC braking system or the supply voltage to the system is too low. SDS can read diagnostic codes from SBC to help pinpoint the problem.
.

 

Bad guess. The oil will circulate even if the pump is weak and the pressure is very low.

I'd still look at pump pressure, testing the throttle valve, and ABC controller fault codes.

 

@sivikvtec and @bobterry99 , thank you for nudging me towards getting diagnostics tool. That was certainly helpful.

I bought C3+DAS and here is what I found:


After clearing the errors and starting the car again only the following would remain as CURRENT:

• "system pressure too low"
• "malfunction in pressure supply"

Actuations would do nothing. I tried:

• leveling the car to calibrated position
• full rodeo
• front-back actuations

nothing would work. That's as expected: the pressure was around 4-5 bars.

I was able to manually actuate valve-blocks and successfully lowered the rear side

I ran pressure-sensor diagnostics, which I assume attempts to lift the car up disregarding the sensor readings. The car didn't go up.

During one of the many car-starts the pressure mysteriously showed-up. It quickly built-up to >150. I didn't do any actuations at that time, but ran sensor test again. As part of the test it showed me the graph with pressure starting from 50 and decaying to 15 over the next few minutes. But the system couldn't build the pressure back up from 15.

That brief moment of pressure being present gave me hope and I tried "priming the pump". I used the hand-pump from my camping-set to build some pressure (no idea how much) in ABC-fluid tank though the dipstick-opening while ignition was off. After doing that and starting the engine immediately afterwards the pressure appeared. I was able to actuate the struts back to normal position!

I experimented:

• starting engine hot or cold without "priming" and pressure wouldn't appear
• tried sealing the dipstick-opening on the ABC-fluid tank hypothesizing the cap wasn't tight - no pressure after starting the engine
• hand-pressurizing the tank and then starting the engine consistently results in pressure appearing in the system

With this, I can level-up the car and drive it around. The rear is rock-solid and does not sag, front sagged ~2cm over the course of the day and driving ~30 miles. While driving I also noticed that on couple engine-starts the red ABC-warning would be gone and I had only grey ABC-warning. I guess these engine-starts randomly produced pressure and "no pressure"-error wasn't current but just stored.

What do these symptoms indicate? If original filter is too dirty, can it cause the pump not start-up correctly? Is the pump dying?

My next planned step is replacing the filter (arriving tomorrow) and doing rodeo to filter the liquid through the new 3mu-filter.

 

A filter that was extremely dirty would restrict the flow of oil returning to the pump reservoir. For it to affect the pump starting the reservoir would have to have run dry. So, I'd say the answer to your question is "no".

A pump that can make no more than 150 bar in a properly-working system is worn, naturally. I'll presume 100 bar is adequate for typical driving, so your pump is probably fine. When I did my most Recent Rodeo pump pressure peaked at 140 bar, dropped steadily, and upon reaching c. 100 bar the routine paused to allow the pressure supply to recover.

 

Thank you. It's good to know that filter is for return. I agree, it doesn't make much sense then for filter condition to affect pump not functioning most of the time without priming.

If pump, with priming, can build sufficient pressure - why would the pump not function without priming?

The only other component directly attached to the ABC-fluid tank (and thus possibly affected by mildly pressurizing the tank) is Y86/1 suction restrictor valve. There was a STORED fault related to it. Can it be at fault?

 

When the pump is replaced it is necessary to prime it for reasons unapparent to me. In your case I have no idea why priming makes a difference, but it is curious that this is necessary and you have a stored fault for the throttle (suction restrictor) valve.

If you double-click on the restrictor valve fault the software will guide you through a test procedure for the valve which is quick and easy to do. That would be my next move.

Also, with those "stored" faults it would be informative to know if they occurred recently or during the Bush administration. Therefore, I would erase all codes from the ABC controller.

Finally, I'm curious about where you purchased your multiplexer and software. I'd appreciate a PM or you can post it to this thread.

 

Dzmitryp -
You're going down the right path with the DAS diagnostic system. Take a look at pages 15-17 of the attached document under Pulsation Dampener / Pressure Check Valve / Pressure Sensor Assembly. In particular, look at paragraphs 3, 4 and 5 here:
"3) The check valve opens at too low a pressure. I don't think it is a likely scenario but it is theoretically possible. In this scenario the control module will sense the need for more pressure and tell the suction valve on the pump to open up, and meanwhile the check valve will constantly route all that extra fluid back to the reservoir in an endless loop. If the pressure that this is occurring at is below the acceptable pressure to operate the ABC system, the control module will shutdown the ABC system and display a warning on the dash. If this endless loop is occurring at a pressure above the minimum but below the ideal, then the system will operate normally but the pump will be working extra hard. I'm guessing the control module would not notice this situation. It won't be able to tell the difference between a weak pump and a check valve letting off pressure too soon. But a constant 5V at the suction valve would indicate the pump is working full throttle all the time.

4) The pressure sensor is not working correctly. It could fail. There could be a loose connection between the sensor and the control module. It could be sluggish in responding to pressure changes. Or it could just be wrong about the pressure it is sensing. The control module should be able to detect a loose connection or a completely failed sensor and log an error code to that effect. That leaves the sensor reporting the wrong pressure. If the sensor is reporting higher then normal, then the control module will be seeing what it thinks are overpressure situations, and will shut down the ABC system and give a dash warning and log error codes. If the sensor is reporting lower pressure than actual, then either 1) in extreme cases the control module will think the system is below normal operating pressure and will shutdown the ABC system along with dash warnings and error codes. It could mimic a pump failure. 2) if a minor case, the normal drops in pressure will be more exaggerated from the control module's perspective, leading to intermittent "drive carefully" messages and occasional ABC system shutdowns.

5) Occasionally the o-ring that provides the seal for the pressure sensor will fail, causing a fluid leak. There is a repair kit available (part number A2203201158) for approximately $80. Don't let the workshop convince you that you need to replace the entire assembly, a $1,250 part."


Here's the document:

 

I did erase the fault codes, and restrictor valve fault has not returned yet (2 days and 30 miles later).

Did that:
1. cold car
2. hand-pumped some air into ABC-fluid tank
3. started the engine
4. took ~10 seconds for pressure to go from 1 to 3, then another 5 seconds from 3 to 70, then a few seconds to go up to 180
5. actuated restrictor valve - and the pressure jumped up ~7 bars for a moment, as expected (the screen instructs that pressure should go up >1 bar when valve is actuated)

Therefore, I am concluding that restrictor valve is fine. I will do the same experiment tomorrow without priming first to see if it will make pressure to appear.

Aliexpress: with D630 laptop. The software was 2019/12 and received it 5 days after placing the order (to Utah).

 

The pump is primed so it doesn't run dry. It would damage itself immediately. At least this is what I was tought.

 

If there is no pressure, then I don't think I have anything else to suggest. You might then join peachparts.com and post your issue in their "Tech Help" forum where it will likely be seen by at least one Mercedes-trained tech (ILUVMILS).

Good luck.

Thanks for the info on where you got your SDS. I asked because it appears not to be running under VMWare, and that is a configuration which I have been unable to find lately on aliexpress.

 

Update:

1. Replaced filter.
2. Did full rodeo: the pressure was between 100 and 130 during the rodeo, quickly recovering to 180-190 after rodeo is complete.

What I'm observing now:

1. Start the engine. Pressure is 1-2 on cold. NO hand-pressurizing this time.
2. ~5 seconds later red ABC error appears on the dashboard. Height-control buttons don't work, of course.
3. SDS is connected, so I can see that pressure starts to go up ~2 seconds after red ABC error shows up. Pressure quickly (<10 seconds) reaches 180-190.
4. At this point I can actuate the height through SDS or, after clearing the fault without ignition ON/OFF-cycle, can use height-control buttons.
5. After restarting the car I'm back to red ABC fault on dashboard.

In short: after replacing the filter and doing rodeo the pressure consistently appears without priming, but it appears too later and system registers "low pressure"-fault, locking the struts and not responding to height-control.

First, I am still puzzled about what the root-cause is. I suspect accumulators. That would explain:

• pressure not building up quickly enough, with pump having to refill them
• ABC-fluid level in the tank certainly having more travel than the marks on the dipstick and fluid overflowing overnight when I initially got the car and added fluid to the level (as it appeared low)

Second, I wonder if the ABC-timeout can be increased to make the system a little more patient while I'm figuring out the root-cause.

Third, is it ok to drive around in the meantime with struts locked (blocking valves closed), and ABC-system not-functioning, but with pressure? If struts are locked, am I stressing them too much without them being connected to accumulators?

 

Your Star Diagnosis can test the accumulators.

Within the ABC menu go to Troubleshooting by means of complaints or symptoms > Handling characteristics > Vehicle damping too soft or spongy handling characteristics > Pressure change during pressure release, and then follow the instructions.

A tech on another forum once encountered your problem, and he attributed it to the pressure sensor being "sluggish". Replacing the sensor was the fix.

Very unlikely, in my opinion. If it is possible, then it would be via the development/engineering menus. I'd look through them, but there are many, many items -- all in German.

Apart from the car handling somewhat poorly, there is no downside to driving with ABC off/faulted.

 

Hi, not very scientific but my car was showing the same symptoms just after I bought it and it went back to the selling garage for warranty repair. They had it about 3 weeks and they couldn’t find the fault and it was also passed to a specialist by them who also couldn’t find the fault.

Eventually, this was their words so no idea of the science involved, it was an “intermittent fault with a valve in the ABC pump”. Their explanation was that the system was losing all pressure intermittently but then immediately restoring full pressure. The drop was sufficient to generate the red warning light and lock the suspension.

They fitted a new ABC pump and it hasn’t reoccurred since. The explanation might not be very accurate from them but your symptoms sound exactly like mine.

 

That's certainly useful to know.

I had supposed taking a chance with replacing the pressure sensor would be the next step, but I don't think so now. A faulty pump could also explain why for a time the reservoir had to be pressurized.

 

@bobterry99 thank you for the recommendation! I did the test:
1. Hand-pumped (pressure didn't appear otherwise, again)
2. Started the engine
3. Waited for pressure to build up to 180
4. Stopped the engine and turned ignition on. Pressure rapidly decreased to ~80
5. Started the test. The car started lowering in some sequence of drops. Below is the screen I got:



My interpretation is: the final pressure is within the expected range. The suggested remedies, based on my limited experience with SDS, are in case the value is outside the range? Or is the "remedy" a dynamic suggestion based on some other values not displayed here?

There is a test in SDS for the sensor: it attempts to actuate the struts disregarding sensor's reading. When sensor was displaying no pressure, the car doesn't move when actuating via SDS. I made the conclusion it's not the sensor.

 

I have an update about my situation. I've replaced the front accumulator and did the fluid flush - both were obviously necessary (accumulator was shot, fluid was black and burnt). These two procedures did not affect the behavior of the ABC system though.

Here is how it behaves now:
- in the morning, now that night temperatures are above freezing, the ABC system does create pressure: I can change height and drive around with ABC operating normally for as long as I want - until I stop the engine
- if starting the car "warm": ABC system does not build the pressure

In other words, the increase in ambient night temperatures made ABC system start fine in the mornings. But if I drive around, stop and start the engine, there is no pressure (1bar), red error, boat ride, height does not change. If I wait a few hours (or overnight) - then I just start the car and ABC system works.

Through trial and error I found a method to make ABC system work even when car is warm:
- start the car
- immediately rev-up to ~2k and hold there for ~5 seconds
- in 8 cases out of 10 on ~2nd second I feel vibration and rumbling sound lasting for a few seconds, at which point the car would level itself
- I am almost certain the sound and vibration are linked to ABC system "starting"

This is super puzzling. From what I can see, ABC pump has no clutch! How can all this be linked? How can an ABC pump (which is always "ON" when engine is "on") sometimes build the pressure and sometime not build it? What's with vibration on the "warm" car when revving-up which makes the ABC system work - what can I be possibly "forcing" to mechanically happen?

I feel that my mental model of the ABC system is wrong somewhere, because what I am observing makes no sense.

 

You can tell whether the oil is circulating and to what degree by removing the ABC reservoir cap and watching the oil drip from the filter. I would compare the flow when the red warning is present with the flow when there is no warning. If you find they are the same, I might be suspicious of the oil pressure sensor or the quality of the electric connection between the ABC controller and its harness.